The invention is concerned primarily with a problem that occurs when the fuel tank is nearly empty and the vehicle is being driven on hilly terrain or winding roads or being held in a sustained turn as when entering a freeway. In such situations the liquid fuel in the tank can either slosh around or be held to one side of the tank so that the fuel pump is momentarily or intermittently deprived of fuel (the pump loses its prime). This condition can occur even though there is some fuel still in the tank; the fuel tank gage can register the existence of fuel in the tank, but still the fuel is not available to the fuel pump.
The problem has been addressed in certain prior art patents.
For example, U.S. Pat. No. 3,443,519 to J. White shows a vehicle fuel system wherein a fuel pump having two tandem arranged pumping impellers is mounted in a casing within the fuel tank. The first impeller pumps fuel from the tank into a reservoir compartments within the casing. The second impeller pumps liquid out of the fuel tank to the engine carburetor or fuel injector mechanism. There is no return flow of excess fuel from the engine to the reservoir compartments. Consequently, the ability of the pump to retain its prime during this fuel starved condition is solely dependent upon the capacity of the reservoir compartment.
Likewise U.S. Pat. No. 4,672,937 to D. Fales shows a fuel supply system including a complex two stage pump and a solenoid actuated valve which, is response to a signal from a cut-off level flow switch, will render the pump first stage inoperative--while rendering the pump second stage operative to draw fuel from a reservoir.
U.S. Pat. No. 4,747,388 to C. Tuckey discloses a fuel supply system comprising a single stage pump and a flexible filter screen which acts not only as the main tank fuel filter but also as a float and valve actuating mechanism to release fuel from the reservoir. Under normal operating conditions fuel will be supplied to the pump through the flexible filter screen. However, should the space below the filter screen become starved of fuel the screen will be lifted causing a valve to open and thereby enabling fuel to flow from a reservoir into the space above the screen and to the pump.